Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. In addition, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (Plug-in HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuels.
In addition, technology related to a power storage device that stores electric power and stably supplies the stored electric power to a power system when needed has been developed. The power storage device is a device that stores electric power when power demand is low and supplies the stored electric power in case of overload or emergency. The power storage device provides the effect of improving quality of electric power and energy efficiency. In particular, a market for a household power storage device and a middle-sized industrial or commercial power storage device has been rapidly expanding as the power storage devices are related to smart grid technology.
Meanwhile, for a battery pack to provide output and capacity required by a predetermined apparatus or device, it is necessary for the battery pack to be configured to have a structure in which a plurality of unit cells or a plurality of battery modules, each of which includes a plurality of unit cells, is electrically connected to each other in series or in parallel. In addition, it is necessary for the battery pack to be configured to have a structure which is easily extendable and stable as the capacity of the battery pack is increased.
Particularly, in a case in which a plurality of battery modules is used to constitute the battery pack, a plurality of members, such as bus bars or power connection cables, for mechanical fastening and electrical connection between the battery modules is generally needed and, as a result, a process of assembling such members is very complicated. Furthermore, in a case in which it is necessary to extend the battery pack, it is difficult to modify the structure of the battery pack and it is necessary to add a plurality of parts, thereby increasing manufacturing cost.
In addition, the battery pack is configured to have a structure in which a plurality of battery modules is combined. In a case in which overvoltage is applied to some of the battery modules, overcurrent flows in some of the battery modules, or some of the battery modules overheat, therefore, safety and operation efficiency of the battery pack are seriously concerned. For this reason, it is necessary to provide a safety system, such as a battery management system (BMS), which detects such overvoltage, overcurrent, or the overheating to interrupt the flow of electric current in the battery pack or operate a cooling device. However, the provision of several sensors and a plurality of wires as well as the BMS increases manufacturing cost and complicates the manufacturing process.
Consequently, there is a high necessity of technology related to a structure that is capable of improving safety of the battery pack during abnormal operation of the battery pack through simple addition or change of parts.